MINNEAPOLIS (WCCO) — A 30-year-old St. Paul man received the longest sentence ever imposed on anyone found guilty of sex-trafficking in Minnesota history.

Otis Deno Washington was found guilty of first- and second-degree solicitation to practice prostitution (one involving a minor), two counts of promotion of prostitution, and one count of conspiracy to commit sex trafficking.

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He was sentenced to 40 years in prison on Thursday morning. Judge Roseanne Nathanson also imposed a lifetime predatory offender registration on Washington.

According to the Ramsey County Attorney’s Office, Washington was involved in a human trafficking operation that lasted for nearly two years between 2010 and 2012.

Washington was the last of four family members to be convicted in connection with the ring. His brother and two of his uncles were charged and convicted as well.

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According to Ramsey County Attorney John Choi, the sex trafficking ring “enslaved numerous women and girls,” some of them who were characterized as mentally vulnerable.

“While we have sent a strong message to human traffickers of children for sex, our work is not done. The sad truth remains that this criminal activity will continue as long as there are vulnerable children who are not identified, helped and protected, as well as men who buy sex on Backpage.com,” Choi said.

Washington and his brother Antonio Dion Washington-Davis were said to have taken drastic measures to keep their victims in line. In April 2011, Washington-Davis brought one victim to a hotel in Ely, Minn., stating it was “somewhere where you can’t talk to any of your family and won’t know where you are.”

Another victim told investigators that both brothers preyed “on young women who are mentally slow and/or vulnerable and recruit them into prostitution.”

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Washington-Davis was sentenced to 36 years in prison last month.